SFA, I don't think you would be "the wicked witch of the west" for asking your husband to cut down a bit on his volunteering. Yes, it's admirable, but your family's needs (and cleaning is a household need) should come before that. It might be a hard conversation to have, but it sounds like that if he is a person who can commit to helping others so much, he would have an open mind to this type of conversation.
I know other people here talked about resenting the fact that they had to help with cleaning chores as kids. I never did, but during the time when we didn't have cleaning help, I did ask my kids to help a bit. They were young (5 and 8) and it lasted for about 2-3 years. I made it a game and we did our work together, at the same time. After that, I expected them to keep their rooms clean (no food left there, garbage) and all of the clutter picked up the night before the cleaning people came. When they turned 13, they had to do their own laundry and put it away. That was a major help, since both of them and my husband wear the same size and we were forever mixing up the socks, underwear, and T shirts.